Electrical gaseous discharge lamp



C. G. SMHTH ELECTRICAL GASEOUS DISCHARGE LAMP Filed Deo. 4, 1940 mvmww.,

emma@ Patented July 16, `1946 ELECTRICAL GASEOUS DISCHARGE LAMP Charles G. Smith, Medford, Mass., assignor to Raytheon Manufacturing Company, Newton, Mass., a corporation of Delaware Application December 4, 1940, Serial No. 368,469

17 Claims. 1

This invention relates to an electrical gaseous discharge lamp.

An object of this invention is to produce such a lamp of high intensity and high efficiency.

Another object is to produce such a lamp which is an effective generator of ultraviolet light.

Another object is to devise a lamp in whichv a localized region of increased conductivity is produced through which the discharge passes for improving the operation of the lamp.

A still further object is to provide a lamp which utilizes a polyatomic gas, such as deuterium, which decomposes into a monatomic gas in the discharge.`

The foregoing and other objects of this invention will be best understood from the following description of an exemplication thereof, reference being had to the accompanying drawing wherein the single iigure is a cross-section of a lamp embodying my invention.

The lamp illustrated consists of an envelope l made of material which is preferably transparent to ultraviolet light, as for example quartz or ultraviolet light transparent glass. Substantially along the central axis of the envelope I is disposed a filament made of a refractory conductor, such as tungsten, and which is designed to operate at about 2000o C. or higher. The lament 2 is supported by lead-in conductors 3-3 sealed through the opposite ends of the envelope l. Each lead-in conductor 3 also carries a small coil of wire 4 which constitutes a self-heating cathode. Each cathode 4 may consist of a coil of thorium Wire, thoriated tungsten wire, or a coil of refractory conducting material coated with an oxide. Also contained within the envelope I is a material 5 whose spectral properties are desired in the discharge, This material may be, for example, antimony, arsenic or mercury. The envelope I also contains a diatomic or polyatomic gas, such as deuterium or hydrogen, which while inert with respect to the electrodes forms volatile compounds with materials such as antimony or arsenic. I prefer to use deuterium which is commonly known as heavy hydrogen. In addition, the envelope I contains an inert gas, such as argon, at a pressure of 1 to 20 mm., e. g. the pressure of the deuterium is preferably lower than the pressure of the argon, e. g. about 1/20 of the argon pressure.

Although the lamp described above may be utilized without an exterior container, in some instances it may be desirable to support it in such a container as illustrated in the drawing.`

As shown, the envelope I is supported within an outer container 6 made of some suitable material, such as glass. The container 6 is provided with a reentrant stem 1. A band 8 is clamped around one end of the envelope I. A pair of standards 9 welded to the band 8 are sealed in the stem l. One of the lead-in conductors'is also sealed in the stem 1. A lead I0 connected to the lead-in conductor 3 extends through the stem 1 to provide an external electrical `connection to'one end of the lament 2. The upper lead-in conductor 3 is connected in series with the resistance II and the standard I2, the lower end of which is also sealed in the stem l. The resistance I I is for the purpose of stabilizing the lamp operation. The standard I2 is provided with an external leadv I3. Where the discharge within the envelope I generates ultraviolet light, it may be desirable to convert such ultraviolet light into visible light. For this purpose the interior walls of the container 6 may be coated with a suitable ucrescent material I4. It is also desirable in some instances to exhaust the tube 5, and for this purpose it is provided with an exhaust tube I5.

When the conductors I0 and I3 are connected to a suitable source of voltage, such as, for example, an alternating current voltage supply, current passing through the lament 2 raises said lament to a temperature of about 2000 or more. At substantially the same time a discharge is initiated between the cathodes 4 through the gaseous atmosphere within the envelope I. Due to this discharge assisted by the heat generated in the filament Y2, the cathodes 4 are raised to temperature of copious thermionic emission so as to maintain the discharge with relatively low cathode drop.

The deuterium or other polyatomic gas mentioned above performs several distinct functions in the lamp. One such function is that it combnes with the antimony or arsenic to form volatile and easily decomposable deuterides, whereby a sufficiently large number of atoms of the material 5 is introduced into the discharge to generate the spectrum of said material to a substantial degree. This aspect of my invention is more fully described and claimed in my copending application, Serial No. 358,848, led September 28, 1940. Also, Vthe hot filament 2 decomposes the diatomic deuterium or other polyatomic gas into a monatomic gas. Hence the region immediately surrounding the filament contains mostly monatomic deuterum. Monatomic deuterium provides a betterpath for conduction of the electrical discharge than 'does the diatomc deuterium. This is also true ofthe other monatomic 3 gases as compared with the polyatomic gases from which they are produced by the heat of the lament 2. As a result of this action, the discharge is concentrated in a localized region within the envelope I along the filament 2.

As between hydrogen and deuterium, deuterium is preferred because of the fact that its atomic weight is twice that of ordinary hydrogen. This makes the deuterium a poorer conductor of heat by a factor of Thus the energy liberated by the filament 2 and by the discharge is conserved along the discharge path increasing the emciency of the discharge and the ease with which ionization and excitation of the atoms in said discharge space are produced. Also the larger atomic weight of deuterium causes the loss due to elastic collisions with velectrons. to be only one-half of such loss in .the case of ordinary hydrogen. However; Where the deuterium is in diatomic form, the loss due. tocollisions is much greater than in the case of monatomic deuterium `thus increasing the tendency for the discharge to concentrate in the region around the lament 2. Also the diusion of the decomposed deuterium away from the region of the filament 2 is times as fast as that of ordinary hydrogen. All of` these eects increase the tendency of the discharge to localize in the region of the filament 2 and to increase the leiectiveness of such discharge; Y

The argon or other inert gas tends to prevent excessive disintegration of the cathode 4. It also assists in the starting of the discharge Where the vapor pressure of the vaporizable material at the start is insuiicient for the desired operation. The inert gas also hinders diffusion of the atomic deuterium away from the region ofthe filament. It alsol acts as a heat-shielding medium for the discharge because it reduces the effective thermal conductivity of the diatomic deuterium.

It is preferable to mount the lamp with its longitudinal axis in a vertical position. In this way circulation of the-gas due to thermal effects tends to take place parallel to the lament and thus avoids a tendency for such circulation of gas to carry the decomposed polyatomic gas away from the regionvof the lament. Also in this position, the -arc does not tend to move over toward the tube side Wall where undesirable heating might take place.

The lamp which I have described above utilizing vaporizable material will operate very much like a vapor lamp of moderate pressure, the arc, however, being localized in the immediate neighborhood of the lament.

Itis to be understood that this invention is not limited to the particular details as described above as many equivalents will suggest themselves to those skilled in the art. For example, in some instances the inert gas may be eliminated. In cases where the inert gas or a component thereof serves as the light emitting medium, the vaporizablematerial may be omitted. Other embodiments utilizing the principles of my invention will suggest themselves to those skilled in the art. It

- is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of theinvention within the art.

What is claimed is: c 1. An electrical discharge device comprlsing an envelope containing a polyatomic gas, thermal means independent of the discharge for decom- Y posing said polyatomic gas into a gas of smaller molecular weight and means for Aproducing an electrical discharge within said envelope.

2. A lamp comprising an envelope containing deuterium, means for decomposing said deuterium into monatomic deuterium along a restricted discharge path spaced from the walls of said envelope, and means for vproducing an electrical dischargek within said envelope through said discharge path.

3. A lamp comprising an envelope containing deuterium, thermal means for decomposing said deuterium into monatomic deuterium and means for producing an electrical discharge Within said envelope.

4. A lamp comprising an envelope containing a gas or vapor whose spectral properties are desirable in said lamp and a polyatomic gas, means independent of the discharge within said lamp for decomposing said polyatomic gas into a gas of smaller molecular weight and means for producing an electrical discharge within said envelope.

5. A lamp comprising an envelope containing a gas or vapor whose spectral properties are desirable in said lamp and a polyatomic gas, thermal means independent of the discharge within said lamp for decomposing said polyatomic gas into a gas of smaller molecular weight and means for producing an electrical discharge within said envelope.

6. A lamp comprising an envelope containing a gas or vapor whose spectral propertiesk are desirable in said lamp and deuterium, means for decomposing said deuterium into monatomic deuterium and means for producing an electrical discharge within said envelope L "I, A lamp comprising an envelope containing a gas or vapor Whose spectral properties are desirable in said lamp and deuterium, thermal means independent of the discharge Within said lamp for decomposing said deuterium into monatomic deuterium, and means Yfor producing an electrical discharge Within said envelope.

8. A lamp comprising an envelope containing a gas or vapor whose spectral properties are clesirable in said lamp and a polyatomic gas, means independent of the discharge within said lamp fordecomposing said polyatomic gas into a gas of smaller molecular Weight along a restricted discharge path spaced from the Walls of said envelope, and means for producing an electrical discharge through said discharge path.

9. A lamp comprising an envelope containing a gas or vapor whose spectral properties are desirable in said lamp and deuterium, means for decomposing said deuterium into monatomic deuterium along a restricted discharge path spaced from the walls of said envelope, and means for producing an electrical discharge through said discharge path.

l0. An electrical discharge device comprising an envelope containing a polyatomic gas, thermal means, independent of the discharge and local ized along a predetermined path for the dis* charge, for decomposing said polyatomic gas into a gas of smaller molecular weight, and means for producing an electrical discharge within said envelope.

11. An electrical discharge device comprising an envelope containing a polyatomic gas, thermal means independent of the discharge arranged to decompose the polyatomic gas along the path of said discharge into a gas of smaller molecular Weight, and means for producing an electrical discharge Within said envelope.

12. An electrical discharge device comprising an envelope containing a polyatomic gas, a thermal lament for decomposing said polyatomic gas into a gas of smaller molecular weight, and means for producing an electrical discharge within said envelope.

13. An electrical discharge device comprising an envelope containing a polyatomic gas, a thermal filament adjacent the discharge path for decomposing said polyatornic gas into a gas ci smaller molecular Weight, and means for producing an electrical discharge within said envelope.

14. An electrical discharge device comprising an envelope containing a polyatomic gas, a thermal filament extending longitudinally along the discharge path and adapted to decompose said polyatomic gas into a gas of smaller molecular weight, and means for producing an electrical discharge within said envelope.

15. A lamp comprising an envelope containing deuterium and a monatomic rare gas of substantially greater molecular Weight than that of the deuteriurn, means for decomposing said deuterium into a gas of smaller molecular weight along a restricted discharge path, and means for producing an electrical discharge through said discharge path.

16. A lamp comprising an envelope containing deuterium and argon, means for decomposing said deuterium into a gas of smaller molecular weight, and means for producing an electrical discharge through said gases.

17. A lamp comprising an envelope containing deuterium and a monatomic gas of greater molecular Weight than that of the deuterium, therma1 means, independent of the discharge within said lamp and localized along a predetermined path in which the discharge is adapted to take place, for decomposing the deuterium along the path of said discharge, and means for producing an electrical discharge through said discharge path.

CHARLES G. SMITH. 

